This invention relates to apparatus for collecting material floating on the surface of a body of water. The apparatus according to the invention can be used for collecting different kinds of pollutants, both solid and liquid, floating on the water, but it is particularly devised and suited for collecting oil spilled on a water surface, including oil mixed with solid material. Hence, the invention will be described with particular emphasis on such use of the apparatus.
More particularly, the invention relates to a skimmer apparatus (skimmer) of the kind adapted to skim a surface layer across a skinning weir of an immersed collection vessel and allow the pollutants to accumulate on the surface of the water in the collection vessel so that they can then be removed in some suitable manner.
WO97/07292 and WO99/22078 disclose prior art embodiments of apparatus of that kind. In this kind of prior art apparatus the collection vessel has a side wall comprising an upper wall part which has some buoyancy and the upper end of which forms the skimming weir, and a lower wall part, the upper wall part being vertically movable relative to the lower wall part. The upper and lower wall parts jointly delimit laterally an upper subcompartment of a collection compartment having an inlet that is formed by the skiimming weir. A lower subcompartment of the collection compartment forms an extension of and is in open communication with the upper subcompartment. Water can be fed into and discharged from the collection vessel through an opening in a bottom wall thereof.
In the apparatus disclosed in WO97/07292 the oil is collected on the surface of the water accommodated in the upper subcompartment of the collection compartment. It is discharged from the collection compartment by feeding water from below into the collection compartment to cause the skimming weir to be pressed against an overlying plate having a discharge opening and cause the oil layer on the water surface to be expelled through the discharge opening into a suitable recipient.
In the apparatus disclosed in WO99/22078, the oil is accumulated in a separation compartment that is delimited laterally between a inner wall, which resembles the side wall of the apparatus according to WO97/07292, and an outer wall. The oil enters across the skimming weir of the inner wall and moves downward in the collection compartment delimited by the inner wall. At the lower edge of the inner wall the oil enters the separation compartment where it accumulates on the surface of the water therein. The separation compartment is delimited upward by a top wall with a discharge opening through which the oil can be expelled in the same manner as in the apparatus according to WO97/07292 by feeding water from below into the collection vessel.
An advantage of positioning the separation compartment outside the collection compartment delimited by the inner wall is that the oil flowing outward from that compartment into the separation compartment is distributed horizontally over an area that can readily be made much larger than the horizontal area delimited by the inner wall. Accordingly, the horizontal velocity of the oil in the separation compartment can be very low, thereby allowing the oil to rise substantially without disturbance to the surface in the separation compartment.
Solid objects of various kinds are often carried along by the oil and cause problems when the oil is to be discharged from the separation compartment. In the apparatus according to WO99/22078, such objects have a tendency to collect at the top of the layer of oil in the separation compartment, adjacent the top wall or roof of the collection compartment, and to remain there when the oil is expelled through the discharge opening. As a result, only those objects which are below or close to the discharge opening are carried along with the oil discharged from the separation compartment.
In the apparatus according to the invention, which is of the kind disclosed in WO99/22078 and thus has a separation compartment that is separated late-rally from the compartment into which the oil flows across the skimming weir, this problem is solved by the design of the apparatus set forth in the independent claim. Advantageous embodiments of the apparatus according to the invention have the features set forth in one or more of the independent claims.